/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds, if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Return the nested list that this NestedInteger holds, if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *     const vector<NestedInteger> &getList() const;
 * };
 */

class NestedIterator {
public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        sta.emplace(nestedList.begin(), nestedList.end());
    }
    
    int next() {
        return (sta.top().first++)->getInteger();
    }
    
    bool hasNext() {
       while (!sta.empty()) {
           auto &temp = sta.top();
           if (temp.first == temp.second) {
               sta.pop();
               continue;
           }
           if (temp.first->isInteger()) return true;
           auto &temp_list = temp.first++->getList();
           sta.emplace(temp_list.begin(), temp_list.end());
       } 
       return false;
    }

private:
    stack<pair<vector<NestedInteger>::iterator, vector<NestedInteger>::iterator>> sta;
};

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i(nestedList);
 * while (i.hasNext()) cout << i.next();
 */